Drive train refers to an abbreviation for a plurality of devices for transferring energy generated by an engine to drive wheels, and is configured by an engine, clutch, transmission, drive shaft, propeller shaft, differential gear, drive wheels, etc. In performance evaluation testing of a drive train, the durability performance, quality, etc. thereof are evaluated by actually continuously driving the transmission by the engine. In recent years, as a system which performs such testing of drive trains, a system has been presented which causes the drive torque inputted on a workpiece to be generated by a motor instead of an actual engine (for example, refer to Patent Document 1).
Since periodic torque fluctuation arises due to the combustion cycle of each cylinder in the actual engine, with the system illustrated in the above-mentioned Patent Document 1, the drive torque generated by the motor is pseudo fluctuated by summing the alternating current component by a sine wave in the direct current component for generating constant drive torque.
However, since a unique vibration mode characterized by a prescribed resonance frequency exists in the above-mentioned such test system configured by joining the test piece and a dynamometer by a shaft, if causing the torque current command signal to the motor to fluctuate periodically, when the frequency thereof passes through the unique resonance frequency in the test system, it may induce resonance vibration. Therefore, with the test system of Patent Document 2, the occurrence of such resonance is suppressed by generating a torque current command signal using a resonance suppression control circuit designed using a control system design method such as H∞ control or μ design.    Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2002-71520    Patent Document 2: PCT International Publication No. WO2015/136626